Alcaftadine is chemically 6,11-dihydro-11-(1-methyl-4-piperidinylidene)-5H-imidazo[2,1-b][3]benzazepine-3-carboxaldehyde and is known from U.S. Pat. No. 5,468,743 and is represented by a compound of structural formula I:

Alcaftadine is a H1 histamine receptor antagonist sold in USA under the proprietary name of “LASTACAFT” and is indicated for the prevention of itching associated with allergic conjunctivitis.
U.S. Pat. No. 5,468,743 describes analogous processes of preparing alcaftadine compound of structural formula I as shown below in scheme no. I, scheme no. II and scheme no. III:



The processes of preparing compound of structural formula VIII according to the above mentioned references produce more than 25% of compound of structural formula XIV:

The compound of structural formula XIV is carry-forwarded into the further steps of reactions of preparing alcaftadine compound of structural formula I and therefore there is a need in the art to develop an improved process of preparing compound of structural formula VIII, which obviates the prior-art problems.
Further, the prior art processes for preparing alcaftadine compound of structural formula I comprises treating compound of structural formula VIII with less than 20 moles of oxidizing reagent which leads to incomplete reaction and causes low yield of alcaftadine.
Accordingly, there is a need in the art to develop an improved process of preparing alcaftadine compound of structural formula I, which obviates the prior-art problems.
The inventors of the present invention have developed an improved process for the preparation of alcaftadine using substantially pure compound or purified compound of structural formula VIII, resulting in higher yield of alcaftadine. The improved process is cost effective and has fewer steps as compared to the process disclosed in the prior publications.
Further, the inventors have found that treating compound of structural formula VIII with more than 20 moles of oxidizing reagent leads to completion of reaction and results in higher yield of alcaftadine.